The proposal will focus on molecular modeling for rational design of dental biomaterials. The five specific aims of this proposal are: 1) to develop a quantitatively useful and predictive model for monomer expansion upon polymerizations; 2) to develop quantitative structure activity relationship (QSAR) models for predicting physical properties of monomers to be used in screening candidates; 3) to develop QSAR models for toxicity of the monomers that will be used to screening candidate structures: 4) to design and optimize potential expanding monomer/matrix resin systems using rational materials design techniques; 5) to design and optimize matrix-compatible adhesive monomers using rational materials design techniques; 6) to develop QSAR models for expansion and stress in a composite formulation; 7) to develop QSAR models for accurate prediction of the behavior of adhesion promoter in dental adhesive formulations, Modern computational chemistry methods employing semi empirical quantum mechanical models along with advanced QSAR approaches will be integrated with experimental information developed as part of the program project. The resulting information will be provided to the projects principal investigators to be used in making decisions to better focus further experimental research efforts. Scientific knowledge will be increased by enhancing understanding of the basic underlying causes of the chemical phenomena of interest in these materials, as well as developing a set of predictive models for future use. The results of this research will improve human health by allowing dental practitioners to apply better materials for more functional and longer-lasting restorations that do not contain mercury.